linux-kernel - Re: perf: use after free in perf_remove_from

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Date:	Thu, 29 May 2014 12:52:53 -0400
From:	Sasha Levin <sasha.levin@...cle.com>
To:	Peter Zijlstra <peterz@...radead.org>
CC:	Ingo Molnar <mingo@...nel.org>, acme@...stprotocols.net,
	LKML <linux-kernel@...r.kernel.org>,
	Thomas Gleixner <tglx@...utronix.de>,
	Dave Jones <davej@...hat.com>
Subject: Re: perf: use after free in perf_remove_from_context

On 05/29/2014 12:50 PM, Peter Zijlstra wrote:
>> > 
>> > So the only caller to sync_child_event() is that loop. According to what you said
>> > it should be safe to remove that mutex lock, but doing that triggers a list
>> > corruption:
>> > 
>> > [ 1204.341887] WARNING: CPU: 20 PID: 12839 at lib/list_debug.c:62 __list_del_entry+0xa1/0xe0()
>> > [ 1204.347597] list_del corruption. next->prev should be ffff8806ca68b108, but was ffff88051a67c398
>> > [...]
>> > 
>> > I don't see how that would happen :/
> No, what I said is that the mutex in perf_event_exit_task() should be
> sufficient to guard the list iteration calling __perf_event_exit_task().
> 
> Ading the RCU was a bit of paranoia.. 

Oh, my bad, I thought you referred to the mutex lock in sync_child_event().


Thanks,
Sasha
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